A meter unit includes a scale plate, a pointer, a stepping motor unit and a central processing unit (i.e., CPU). The CPU controls the stepping motor unit, so that the stepping motor unit rotationally drives the pointer on the scale plate. The meter unit according to a prior art has a problem that the pointer indicates (i.e., points to) an incorrect value, which deviates from a correct value. Here, the correct value is a detected value of a physical quantity detected by an outside physical quantity sensor. Specifically, the pointer indicates a misdirected position, which deviates from a correct position. The correct position is a target position, which shows the correct value.
This indication deviation arises from several positioning deviations and the like. For example, when the pointer is mounted on the stepping motor unit, the positioning between the pointer and the stepping motor unit has a certain deviation, which causes the indication deviation. Further, when the scale plate is mounted on the stepping motor unit, the positioning between the scale plate and the stepping motor unit has another certain deviation, which also causes the indication deviation. Therefore, the meter unit has a proper indication deviation.
In view of the above problem, a meter unit having a memory for storing (i.e., memorizing) an indication deviation data of the meter unit is disclosed in Japanese Unexamined Utility Model Application Publication No. H03-4218. A CPU of the meter unit controls a stepping motor unit in consideration of the stored deviation data in such a manner that a detected value detected by a sensor is compensated with the stored deviation data. Thus, a pointer indicates a correct value, which is the detected value.
However, if a part of the meter unit such as the stepping motor unit, the CPU, and the memory fails after the meter unit is delivered to a market place, the whole meter unit is necessitated to exchange for repairing the meter unit. That is because it is difficult to exchange only a failed part of the meter unit. Specifically, only the failed part of the unit cannot be detached from the meter unit so as to repair the failed part. Thus, the whole meter unit is required to detach and exchange. Therefore, a maintenance cost of the meter unit becomes higher.